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Re: How to avoid common subexpression elimination under this situation?

From: Paolo Bonzini <bonzini at gnu dot org>
To: Bingfeng Mei <bmei at broadcom dot com>
Cc: gcc at gcc dot gnu dot org
Date: Tue, 23 Oct 2007 14:18:19 +0200
Subject: Re: How to avoid common subexpression elimination under this situation?
References: <2E073B3ABB3F664DBA1D1C4D5FB47EF405646F9C@NT-IRVA-0752.brcm.ad.broadcom.com>

In RTL level, it is difficult to reverse the optimization. In our 3.4.6
-based porting, the GCC actually generates the latter code. How to
avoid CSE under such situation? Any suggestion is greatly appreciated.

You are probably not defining the ADDRESS_COST or (if you have no ADDRESS_COST hook at all) the RTX_COSTS hook properly. Addressing mode selection is done at RTL-level. In 4.2.1 the RTL CSE pass will undo the CSE (yes, I know it's confusing!...) if the hooks are implemented properly; in 4.3.0 it will be fwprop who does the CSE undoing.

Paolo

References:
- How to avoid common subexpression elimination under this situation?
  - From: Bingfeng Mei

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